Degradation of surfactant protein D by alveolar macrophages.
Surfactant protein (SP) D is a pulmonary surfactant-associated protein that may function in lung host defense. SP-D is produced by alveolar type II cells and nonciliated bronchiolar epithelial (Clara) cells of the airway and is secreted into the air space. Here we investigated whether alveolar macrophages degraded SP-D in vitro. We also examined the effects of SP-A and lipids on SP-D metabolism. The results showed that alveolar macrophages bound and degraded SP-D in a time- and temperature-dependent fashion. After 100 min of incubation, the formation of trichloroacetic acid-soluble degradation products increased 4-fold in the medium and 30-fold in the cells. The degradation of SP-D was via a cell-associated process because SP-D was not degraded when incubated in medium previously conditioned by alveolar macrophages. Gel autoradiography of cell lysate samples after incubation with 125I-labeled SP-D demonstrated an increase in degradation products, further confirming the degradation of SP-D by alveolar macrophages. In addition, the degradation of SP-D was not affected by coincubation with SP-A or surfactant-like liposomes containing either phosphatidylglycerol or phosphatidylinositol. In conclusion, alveolar macrophages rapidly degrade SP-D and may play an important role in SP-D turnover and clearance.
Dong
Q
Q
Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Wright
J R
JR
D000818:Animals; D016466:CHO Cells; D002478:Cells, Cultured; D006224:Cricetinae; D006023:Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011510:Proteolipids / Q000494:pharmacology; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014162:Transfection; D014316:Tritium
D006023:Glycoproteins; D008081:Liposomes; D011510:Proteolipids; D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D011994:Recombinant Proteins; D014316:Tritium